Field of the Invention
The invention relates to a complementary metal oxide semiconductor (CMOS) transistor and a fabricating method thereof. More particularly, the invention relates to a CMOS thin film transistor (TFT) and a fabricating method thereof.
Description of Related Art
Due to the rising consciousness of environmental protection, flat display panels featuring low power consumption, optimal space utilization, no radiation, and high image quality have gradually become the mainstream products of the market. Common flat panel displays include liquid crystal displays (LCD), plasma displays, organic electroluminescent displays, and so forth. The most common LCD, for instance, is mainly comprised of a TFT array substrate, a color filter substrate, and a liquid crystal layer sandwiched between the two substrates. In the conventional TFT array substrate, the amorphous silicon (a-Si) TFT or the low temperature polysilicon (LTPS) TFT often serves as the switch device of each sub-pixel. According to the recent researches, the amorphous oxide TFT has greater mobility than the a-Si TFT and has the superior threshold voltage variation than the LTPS TFT due to no grain boundary effects. Accordingly, the oxide TFT has great potential for becoming the key element of the next-generation flat panel display.
In the TFT array substrate, both a p-type TFT and an n-type TFT, forming the CMOS circuits, an output buffer, a shift register, or other driving circuits et al., need to be formed on the TFT array substrate in order to reduce power consumption. By forming the p-type TFT and the n-type TFT at the same time, the system-on-glass (SOG) concept, i.e. forming system circuits on the glass substrate, can be accomplished. The p-type or n-type semiconductor characteristics of the oxide TFT are determined based on the material of the channel layer, which is different from the LTPS TFT whose n-type or p-type TFT characteristics are determined by ion implantation. When the p-type channel layer of the p-type oxide TFT is in contact with the n-type channel layer of the n-type oxide TFT in the manufacturing process, the p-type channel layer and the n-type channel layer may affect each other. As such, the inherent semiconductor characteristics of the p-type channel layer and the n-type channel layer are changed. Besides, when one of the p-type and n-type oxide TFTs is etched, the other, if coming into contact with the etchant, may be damaged. Accordingly, how to mitigate or even prevent mutual influence between the p-type channel layer and the n-type channel layer is one of the main issues to be resolved by people skilled in the art.